In methods of forming a dye image by using a light-sensitive silver halide color photographic material, the dye image is usually formed by reacting, after imagewise exposure, an oxidized p-phenylenediamine color developing agent with a dye image forming coupler. In such methods, color reproduction is commonly carried out by applying the subtractive color process, where cyan, magenta and yellow dye images corresponding to red, green and blue are formed in respectively corresponding light-sensitive layers. In recent years, in forming such dye images, it has become common to carry out development processing at higher temperatures and lessen certain processing steps, in order to shorten the steps for development processing. In particular, in order to shorten the development processing time by carrying out the development processing at high temperatures, it is very important to increase the developing speed in color developing. The developing speed in color developing is influenced from two directions. One of them is light-sensitive silver halide color photographic materials and the other of them is color developing solutions.
In the former, particularly the shape, size and composition of the grains of light-sensitive silver halide emulsions used may greatly influence the developing speed. In the latter, conditions of color developing solutions, in particular, types of development restrainers tend to influence the developing speed. In particular, silver chloride grains are known to exhibit a remarkably high developing speed under specific conditions.
For this reason, light-sensitive silver halide color photographic materials having silver halide emulsion layers containing silver halide grains substantially consisting of silver chloride (hereinafter "light-sensitive silver chloride color photographic materials"), which can achieve much faster processing than the conventional light-sensitive materials that employ silver chlorobromide, are greatly advantageous for carrying out the processing in a short time, minimizing automatic processors, reducing development replenishing solutions, and further decreasing the burden to environmental pollution when used in miniature photofinishing laboratories which have been recently highlighted. Accordingly various studies have been made to put them into practical use, as having been demonstrated in all sorts of publications, patents and so forth.
However, the light-sensitive silver halide color photographic materials containing silver halide grains substantially consisting of silver chloride were found to cause a great variation in speed (sensitivity) or gradation depending on exposure illuminance, as compared with light-sensitive color photographic materials containing silver halide grains having other composition.
It is a hitherto well-known phenomenon that the speed changes as the illuminance varies, even under the same amount of exposure. Hence, countermeasures have been taken such that the amount of exposure is varied corresponding to a previously estimated change in speed, thus bringing about no particular serious obstacles from a practical viewpoint.
Nonetheless, in instances in which the variation of gradation by exposure illuminance (hereinafter called "illuminance dependence of gradation") is large, the change turns to a fatal defect from the view point of the quality of light-sensitive materials. The light-sensitive materials differ in their desired gradation depending on what they are used for, and they are designed to give a correspondingly different gradation. When these light-sensitive materials are actually exposed to light, the exposure illuminance changes as a matter of course depending on exposure conditions as exemplified by the lightness of an object in the case of light-sensitive materials used in taking photographs, or the difference in image density due to over- or under-exposure of original image films in the case of light-sensitive materials used in printing. In the case of light-sensitive material having a large illuminance dependence of gradation, the gradation actually obtained may deviate from the tolerance range of the designed target gradation, depending on the degree of exposure illuminance.
This may result in an excessively high contrast depending on scenes to give no representation particularly at low-density portions and high-density portions, or, on the contrary, an excessively soft contrast to give no sharpness with a feeling of an out-of-tone, bringing about a serious loss of the quality as light-sensitive material in both cases.
Moreover, in the case of the light-sensitive materials used in printing, they have a variety of print size, including, among those commonly used, the small-sized ones of so-called E-size and even those of the full-length size. Usually users often try first printing out a film of several scenes, select preferred scenes from among them, and enlarge them to a larger size. In this occasion, the original image film used in the printing to a small size is the same as in the printing to a large size and also it is difficult to steeply increase the intensity of a light source, so that making enlargement to a large-sized print may inevitably result in a lowering of the exposure illuminance on the printing light-sensitive materials. As a result, when the illuminance dependence of gradation is large, the image quality is worsened in large-sized prints even though a preferable image quality can be obtained in small-sized prints, thus making it unable to satisfy the users.
An improvement in exposure apparatus has brought the change in speed depending on exposure illuminance to cause no particular serious problems as previously mentioned above, but it is very difficult to cope with the change in gradation by improving equipments such as exposure apparatus. Accordingly, an improvement in the illuminance dependence of gradation is sought from the direction of light-sensitive materials.
As techniques for improving such illuminance dependence, a technique to improve it by using iridium compounds has already been disclosed, for example, in Japanese Patent Publications Open to Public Inspection [hereinafter referred to as Japanese Patent O.P.I. Publication(s)] No. 97648/1986, No. 93448/1986 and No. 3536642/1986. The present inventors, however, have ever made studies on these techniques to find that in respect of silver halide emulsions "substantially" consisting of "silver chloride", the illuminance dependence is less improved by using iridium compounds, than in respect of those comprising silver chlorobromide having a silver chloride content of 90 mol % or less, silver bromide, silver iodobromide or the like. They further have found that the resistance to pressure is deteriorated because of the use of iridium compounds in the case of silver halide emulsions substantially consisting of silver chloride. An improvement in the pressure resistance by the use of iridium compounds is disclosed in Japanene Patent O.P.I. Publication No. 51733/1981, but it was quite unexpected that the pressure resistance is deteriorated on the contrary. As a result of studies, this also was found to be presumably inherent in the silver halide emulsions containing silver chloride in a large amount, but the deterioration of pressure resistance is even fatal as manufactures.
Namely, this is because, with achievement of rapid processing and spread of miniature photofinishing laboratories, light-sensitive materials tend to be applied with pressure and stress in a stronger and more various manner, and are thus required to have resistance also to the pressure.
A number of reports have been made on researches relating to the fact that this physical pressure causes fog or desensitization in silver halide emulsions that constitute the light-sensitive materials.
For example, D. Dautrich, F. Granzer and E. Moisar, The Journal of Photographic Science, Vol. 21 (1973), p. 221-226, makes a detailed report on the deformation of silver halide grains owing to pressure, the strain or lattice defects in crystals under such a state, and the influence which these may give to the distribution of latent image centers.
As a means for improvement to cope with this pressure fog or pressure desensitization, hitherto known is a method by which the pressure is made not to reach silver halide grains, i.e., a method in which various gelatins, polymer, surfactants or other various organic matters are used in a protective layer or intermediate layer of light-sensitive materials and a layer containing silver halide grains.
For example, methods are known in which used are heterocyclic compounds, as in British Patent No. 738,618, alkylphthalates, as in British Patent No. 738,637, alkyl esters, as in British Patent No. 738,639, hydrophilic compounds, in particular, polyhydric alcohols, as in U.S. Pat. No. 2,960,404, carboxyalkyl celluloses, as in U.S. Pat. No. 3,121,060, paraffins and carboxylic acid slats, as in Japanese Patent O.P.I. Publication No. 5017/1974, glycerol derivatives and ether or thioether compounds, as in Japanese Patent O.P.I. Publication No. 141623/1976, organic high-boiling compounds not miscible with hydrophilic binders, as in Japanese Patent O.P.I. Publication No. 85421/1978, and alkyl acrylates and organic acids, as in Japanese Patent Examined Publication No. 28086/1978, respectively.
However, the present state of things is that these passive methods are almost ineffective to a strong pressure against light-sensitive materials, and may rather result in an excessive stickiness given on the surfaces of light-sensitive materials or bring about an adverse influence such as sensitization, desensitization, change of gradation or fog against the performances of light-sensitive materials, thus not sufficiently achieving what is originally aimed therein.
Thus, the present inventors were urged to make compatible the illuminance dependence and pressure resistance, and made studies on various additives. In the course of the studies, the effect to improve pressure resistance was found to be obtainable by using a mercapto compound having the product of solubility (K.sub.PS) to silver ions, of 10.sup.-12 or less, among nitrogen-containing heterocyclic compounds used as growth modifiers or stabilizers during the formation of grains. Since, however, the effect was still insufficient, they intensively made further studies to find that the pressure resistance can be remarkably improved by forming the grains under an acidic condition. This was found to be effective also to the illuminance dependence.